The present invention relates to gas-operated, autoloading shotguns, and it relates more particularly to an improved autoloading gas-power system therefor.
Gas-operated firearms usually include a receiver and a breech-bolt mechanism mounted for reciprocal movement to and from battery position in the receiver. The bolt mechanism is mechanically linked to a piston and cylinder assembly which is automatically operated by a portion of the pressurized gas developed on discharge of a round and bled from the gun barrel to the cylinder. Energy of the pressurized gas is converted into mechanical energy through movement of the piston that is utilized to mechanically unlock the bolt mechanism after firing, withdraw the bolt mechanism from battery position, eject the spent shell, and advance a fresh shell into position for loading into a breech chamber. Simultaneously, an action spring coupled to the bolt mechanism is compressed. Subsequently, the action spring returns the bolt mechanism to the battery position, loading the fresh shell into the breech chamber.
The basic design and principles of operation of autoloading, gas-operated firearms are well known. However, certain difficulties have been encountered in prior gas-operated shotguns, one of which has been in providing a gas-system which is efficient and reliable, while at the same time permits the firearm to be acceptable in appearance, have good balance, and proper "feel" when handled by the shooter. It is also generally recognized that in order to obtain the desired magazine capacity, reliable feeding of the cartridge from the magazine to the cartridge chamber and proper balance of the firearm, it is essential to use a tubular magazine mounted below and parallel to the barrel within the so-called forend of the gun.
The location of the magazine as well as the arrangement and location of the piston-cylinder assembly all play an important role in determining the balance, sighting, and "feel" characteristics of the gun. Another basic problem encountered in the design of a suitable gas-operated shotgun with a tubular magazine is that, in order to fire both low and high power ammunition, the gas cylinder must be mounted where the magazine tube is located and the piston must have sufficient cross-sectional area to provide the power needed to compress the action-return spring, as well as to overcome the friction and other resistance to movement of the bolt when low-power cartridges are fired.
The U.S. Pat. to Hillberg No. 2,909,101 discloses one way of overcoming this problem by placing an annular piston around the outside of the magazine with an annular cylinder similarly mounted so that the gas take-off can be located at the required distance from the cartridge chamber without shortening the magazine. In this arrangement the annular piston surrounding the magazine tube provides the needed piston area without having to increase the size of the forend so much that the gun is undesirably bulky in the forend and awkward to handle. One of the difficulties with the Hillberg design is that the annular piston must have a gas-tight fit with the magazine tube on which it slides. This requires close manufacturing tolerances in order to maintain concentricity and alignment between the piston and the magazine tube over the full distance the piston travels with the action of the gun. Any out-of-roundness of the magazine or other deformation results in binding of the annular piston. But even when alignment is good and tolerances are met, an undesirable amount of wear occurs between the piston and the magazine tube due to the tight fit which the piston must have with the outer surface of the tube. Furthermore, in annular-piston gas systems, such as that of Hillberg as well as that of the short-stroke annular-piston designs of Kelly et al U.S. Pat. No. 3,200,710 and Zanoni 3,848,511, there is inherently a substantial loss of power due to leakage of gas between the magazine tube and the piston and between the piston and the outer walls of the cylinder.
Alternative arrangements have been to mount the gas piston and cylinder within the magazine tube, as disclosed in the U.S. Pat. to Sefried No. 2,482,880, or to mount them in front of the magazine as disclosed in U.S. Pat. No. 3,680,433 to Tollinger. However, these designs reduce the capacity of the magazine due to the fact that the gas take-off port must be located relatively near the shell chamber in order to operate satifactorily with low-power ammunition. Another alternative is to mount the gas piston and cylinder around the barrel as shown in U.S. Pat. to J. E. Browning No. 2,252,754. This arrangement, however, is not satisfactory for a sporting arm because of the bulkiness of the piston and cylinder on the barrel, which not only is unpleasant in appearance, but also prevents proper sighting of the gun.
It is an object of the present invention to provide a gas-operated autoloading shotgun equipped with a compact gas-power system having excellent feel and balance. It is also an object of the invention to provide an improved gas-power system that is reliable in operation and economical to manufacture and maintain.